Integration by substitution

Converts a definite integral of a composite function into an integral over a new variable by substituting t = φ(x). It is used to simplify integrals whose integrand contains a function and its derivative.

\int_a^b f(\phi(x)) \phi'(x) \, \mathrm{d}x = \int_{\phi(a)}^{\phi(b)} f(t) \, \mathrm{d}t

What the symbols mean

a continuous function being integrated
a continuously differentiable substitution function of x
the derivative of \phi with respect to x
lower limit of integration in x
upper limit of integration in x
the new integration variable, t = \phi(x)

About this formula

  • FieldMathematics
  • TopicIntegration techniques
  • LevelUniversity
  • Also calledu-substitution, reverse chain rule, change of variables, substitution rule for definite integrals, u-substitution formula, change of variables in integral
  • SourceWikidata Q1071270

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